Bolivia's former president Jorge Quiroga (R) speaks next to Colombia's former president Andres Pastrana during a news conference in Caracas May 28, 2015. REUTERS/Marco Bello

CARACAS (Reuters) - Venezuela blocked two former Latin American presidents on Friday from visiting opposition leaders jailed a year ago for their roles in deadly protests against the government of socialist President Nicolas Maduro.

Andres Pastrana of Colombia and Jorge Quiroga of Bolivia, both political conservatives, were not allowed to meet opposition leader Leopoldo Lopez and former mayor Daniel Ceballos.

“This is the second time they did not let us through ... but we will be here again,” Pastrana told reporters, referring to a prior visit in January when he attempted to see Lopez.

Lopez is being held in the Ramo Verde military prison outside Caracas, while Ceballos is in a civilian prison in the central state of Guarico.

The presidents, in the company of family members, attempted to visit both sites.

”Once again, you are witnesses to the fact that Leopoldo Lopez has been kidnapped,“ his wife, Lilian Tintori, said. ”The order not to let us in came from above.

Lopez is on trial for inciting protests that sparked three months of violent demonstrations against Maduro during which 43 people died, and of being responsible for damages to government property.

Ceballos, who was mayor of the western city of San Cristobal near the border with Colombia, is accused of supporting street blockades and calling for violence during those same protests. His trial is also continuing.

International rights groups and human rights organizations have called on Maduro to free politicians jailed on charges of trying to destabilize the country. Maduro has responded that the country’s justice system is autonomous and that the people in question are criminals.

State ombudsman Tarek Saab said the former presidents were part of an “international campaign” and a “media war” against Venezuela.

“They have come to give our country human rights classes,” Saab said during a news conference. “No foreigner, even if they are an ex-president, has the moral authority to carry out any (such) campaign.”